A LED lamp or LED light bulb is an electric light for use in light fixtures that produces light using light-emitting diode (LED). LED lamps have a lifespan up to 25 times longer than incandescent lamps, and are significantly more efficient than most fluorescent lamps,[1][2][3] with some LED chips able to emit up to 303 lumens per watt (as claimed by Cree and some other LED manufacturers).[4] However, LED lamps require an electronic LED driver circuit when operated from mains power lines, and losses from this circuit mean the efficiency of the lamp is lower than the efficiency of the LED chips it uses. The most efficient commercially available LED lamps have efficiencies of 200 lumens per watt (lm/w).[5][6][7] Commercially available LED chips have efficiencies of over 220 lm/w.[citation needed] The LED lamp market is projected to grow by more than twelve-fold over the next decade, from $2 billion in the beginning of 2014 to $25 billion in 2023, a compound annual growth rate (CAGR) of 25%.[8] As of 2016, LEDs use only about 10% of the energy an incandescent lamp requires.[9]

Similar to incandescent lamps and unlike most fluorescent lamps (e.g. tubes and compact fluorescent lamps or CFLs), LEDs come to full brightness without need for a warm-up time; the life of fluorescent lighting is also reduced by frequent switching on and off.[10] The initial cost of LED is usually higher. Degradation of LED dye and packaging materials reduces light output to some extent over time.

Some LED lamps are made to be a directly compatible drop-in replacement for incandescent or fluorescent lamps. An LED lamp packaging may show the lumen output, power consumption in watts, color temperature in kelvins or description (e.g. "warm white", "cool white" or "daylight"), operating temperature range, and sometimes the equivalent wattage of an incandescent lamp of similar luminous output.

Most LEDs do not emit light in all directions, and their directional characteristics affect the design of lamps, although omnidirectional lamps which radiate light over a 360° angle are becoming more common. The light output of single LED is less than that of incandescent and compact fluorescent lamps; in most applications multiple LEDs are used to form a lamp, although high-power versions are becoming available.

LEDs, as their name suggests, operate as diodes and run on direct current (DC), whereas mains current is alternating current (AC) and usually at much higher voltage than the LED can accept. Although low voltage LED lamps are available, LED lamps can contain a circuit for converting the mains AC into DC at the correct voltage. These circuits contain rectifiers, capacitors and may have other active electronic components, which may or may not permit the lamp to be dimmed.